JP2013231824A - Electrophoretic display device and drive method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow for easy and precise gradation control of a target pixel.SOLUTION: A drive circuit of an electrophoretic display device includes the steps of: applying a first voltage pulse to a target pixel for only the number of times determined according to a target gradation of the pixel to thereby cause the pixel to transit to a first display state; and applying, for only the number of times according to a gradation distance to the target gradation, a second voltage pulse that has a reverse polarity to that of the first voltage pulse and a smaller amount of change in gradation per scan than the first voltage pulse if the direction of the target gradation is opposite to the direction of gradation changed by the first voltage pulse when viewed from the first display state. The drive circuit further includes a step of applying, for only the number of times according to the gradation distance to the target gradation, a third voltage pulse that has the same polarity as that of the first voltage pulse and a smaller amount of change in gradation per scan than the first voltage pulse if the direction of the target gradation is same as the direction of gradation changed by the first voltage pulse when viewed from the first display state.

Description

  The present invention relates to an electrophoretic display device that reversibly changes a visual state by the action of an electric field or the like and a driving method thereof.

  Conventionally, as a method of controlling the gradation of an electrophoretic display device, a method of applying a voltage between electrodes of a target pixel while controlling the pulse length of a driving pulse (see, for example, Patent Document 1), and changing the pulse length. Instead, a method of performing gradation display by controlling only the number of times of applying the drive pulse between the electrodes of the target pixel (number of times of application) has been proposed (for example, see Patent Document 2). In the driving method described in Patent Document 1, a reset voltage is written to each pixel electrode in the reset period Tr, and then in the write period, a period according to the gradation value indicated by the image data. Only an applied voltage is applied to each pixel electrode. Thereafter, a common electrode voltage is written to each pixel electrode, whereby electric charges accumulated in the pixel capacitor are discharged, and an electric field is applied to the dispersion system. Thereafter, the display image is held. In addition, the driving method described in Patent Document 2 includes a plurality of first particles that have relatively high mobility and are negatively charged, and a plurality of second particles that have relatively low mobility and are positively charged. In the structure in which the electrophoretic layer is sandwiched between the first electrode and the second electrode arranged to face each other, the first electrode has a relatively higher potential than the second electrode between the first electrode and the second electrode. A voltage is applied, and then a pulsed second voltage in which the first electrode is relatively lower in potential than the second electrode is intermittently applied a plurality of times between the first electrode and the second electrode. Each of the applied second voltages has substantially the same pulse width and substantially the same voltage value, and the number of times of application of the second voltage is set according to the gradation.

JP 2002-116733 A JP 2009-237543 A

However, the drive method described in Patent Document 1 described above requires precise control of the length of an extremely short pulse in order to achieve a linear gradation change in a range from pure black display to pure white display. It was difficult to express multiple gradations.
Further, in the driving method described in Patent Document 2 described above, in order to realize multi-gradation display, it is necessary to apply a pulse many times at a high speed. Performance was required.

  The present invention has been made in view of such problems, and can achieve multiple gradations without increasing the required performance for a switching element or driver that controls the pulse length or application timing applied to the pixel electrode, An object of the present invention is to provide an electrophoretic display device capable of displaying a high-quality image and a driving method thereof.

  An electrophoretic display device according to the present invention includes a pair of substrates, at least one of which has light transmissivity, a plurality of pixel electrodes formed on a substrate surface of one of the pair of substrates, and the pair of substrates. Disperse at least two kinds of charged particles having different moving speeds enclosed in a space formed between the pair of substrates and a common electrode formed on the surface of the other substrate facing the plurality of pixel electrodes. A voltage pulse that generates a potential difference for moving the charged particles between the liquid electrode and the pixel electrode and the common electrode, and a selection signal that selects a target pixel to which the voltage pulse is to be applied. A driving circuit that applies a first voltage pulse to the target pixel a number of times determined according to a target gradation of the pixel and makes a transition to the first display state. Table of If the target gradation is in the direction opposite to the gradation change direction by the first voltage pulse as seen from the state, the first voltage pulse has the opposite polarity and the gradation change amount per time is the first voltage. A second voltage pulse smaller than the pulse is applied the number of times corresponding to the gradation distance to the target gradation, and the target gradation is the same as the gradation change direction by the first voltage pulse as seen from the first display state. The third voltage pulse having the same polarity as the first voltage pulse and having a smaller gradation change amount per time than the first voltage pulse in accordance with the gradation distance to the target gradation. It is characterized by applying the number of times.

  With this configuration, the first voltage pulse has a polarity opposite to that of the first voltage pulse, and the second voltage pulse whose gradation change amount per time is smaller than that of the first voltage pulse. Gradation control is performed in combination with a third voltage pulse that has the same polarity as the voltage pulse and the gradation change amount per time is smaller than that of the first voltage pulse, so the length of the extremely short pulse can be precisely controlled. Alternatively, it is not necessary to apply the pulse many times at high speed, and multiple gradations can be realized without increasing the required performance for the switching element or driver for controlling the pulse length or application timing applied to the pixel electrode.

  In the electrophoretic display device, the driving circuit generates a voltage pulse having a pixel selection time shorter than that of the first voltage pulse as the second and third voltage pulses. As a result, the first voltage pulse and the voltage pulse having a pixel selection time shorter than that of the first voltage pulse are combined and gradually approached to the target gradation. Therefore, the length of the extremely short pulse is precisely controlled. Compared to the case where the target gradation is reached, the required performance for the switching element or driver can be relaxed.

  In the electrophoretic display device, a voltage pulse having the same pixel selection time as the first voltage pulse is generated as the second and third voltage pulses, and the second and / or third voltage pulses are applied in a plurality of levels. In this case, the repetition period is longer than the repetition period of the first voltage pulse. As a result, since the voltage pulse having the same pixel selection time as the first voltage pulse is used as the second and third voltage pulses, the minute selection is made depending on the type of TFT or the like and the transfer speed of the image data of the display image. The present invention can be applied when writing by time (for example, 10 μs) is difficult to realize.

  In the electrophoretic display device, charged particles having a low moving speed may be concentrated on an electrode on the substrate side having light permeability. Thereby, the transition time from the initial state to the desired gradation display can be shortened.

  In the electrophoretic display device, a shaking pulse in which the polarity of the voltage is alternately inverted is applied between the pixel electrode and the common electrode of each pixel to all the pixels to be controlled or all of the pixels in the predetermined area. You may do it. As a result, charged particles that have been left for a long time by applying a shaking pulse can be loosened, and the charged particles can be moved more easily by a write pulse applied thereafter.

  According to the present invention, multiple gradations can be realized and a high-quality image can be displayed without increasing the required performance for a switching element or driver that controls the pulse length or application timing applied to the pixel electrode.

1 is an overall configuration diagram of an electrophoretic display device according to an embodiment. It is a circuit diagram which shows the electrical structure of the pixel in the said electrophoretic display device. It is a fragmentary sectional view of the display part in the above-mentioned electrophoretic display device. It is a flowchart which shows the gradation control in 1st Embodiment. It is a figure which shows the transition state of the gradation change in 1st Embodiment. It is a figure which shows the characteristic of the reflectance change by a black reference | standard and a white reference | standard. It is a figure which shows the combination of the voltage pulse which implement | achieved the gradation change shown in FIG. It is a flowchart which shows the gradation control in 2nd Embodiment. It is a figure which shows the transition state of the gradation change in 2nd Embodiment. It is a figure which shows the combination of the voltage pulse which implement | achieved the gradation change shown in FIG. It is a figure which shows the voltage change between electrodes at the time of applying a standard selection pulse repeatedly by the scanning period T and the scanning period T2.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is an overall configuration diagram of an electrophoretic display device according to a first embodiment of the present invention. The electrophoretic display device 1 includes a display unit 2 in which pixels are arranged in a matrix, a data line driving circuit 3 that supplies an image signal to the display unit 2, and a scanning line driving circuit 4 that supplies a scanning signal to the display unit 2. And a common potential supply circuit 5 that applies a common potential to each pixel of the display unit 2 and a controller 6 that controls the operation of the entire apparatus. Among these, the data line driving circuit 3, the scanning line driving circuit 4, the common potential supply circuit 5, and the controller 6 constitute a driving circuit.

  In the display unit 2, n data lines X 1 to Xn extending in parallel in the column direction (Y direction) extend from the data line driving circuit 3, and intersect with these data lines from the scanning line driving circuit 4. The m scanning lines Y1 to Ym extend in parallel in the row direction (X direction). In the display unit 2, pixels 20 are formed at each intersection where the data lines (X1, X2,... Xn) and the scanning lines (Y1, Y2,... Ym) intersect. Thus, the display unit 2 has a plurality of pixels 20 arranged in a matrix of n rows and m columns.

  The data line driving circuit 3 supplies an image signal to each data line (X1, X2,... Xn) based on the timing signal supplied from the controller 6. The image signal takes a high potential VH (for example, 30 V) or a low potential VL (for example, 0 V).

  The scanning line driving circuit 4 sequentially supplies a scanning signal having a fixed pulse width to each scanning line (Y1, Y2,... Ym) based on the timing signal supplied from the controller 6. Thereby, a scanning signal is supplied to the pixel 20 to be driven. Since a pixel to be subjected to gradation control is selected by the scanning signal, the scanning signal can also be called a selection signal.

  A common potential Vcom is applied from the common potential supply circuit 5 through the common potential line 11 to each pixel 20 constituting the display unit 2. The common potential Vcom is a high potential VH (for example, 40 V) or a low potential VL (for example, 0 V).

  The controller 6 supplies timing signals such as a clock signal and a start pulse to the data line driving circuit 3, the scanning line driving circuit 4, and the common potential supply circuit 5 to control each circuit. The controller 6 supplies the gradation data of the target pixel to the data line driving circuit 3 or the common potential supply circuit 5. The data line driving circuit 3 or the common potential supply circuit 5 determines the number of application of the write pulse and the voltage value according to the gradation data, and outputs an image signal to the target pixel in synchronization with the pixel row selection operation of the scanning line driving circuit 4. Alternatively, a common potential is supplied.

  FIG. 2 is an equivalent circuit diagram illustrating an electrical configuration of the pixel 20. Since each pixel 20 arranged in a matrix on the display unit 2 has the same configuration, each unit constituting the pixel 20 will be described with a common reference numeral.

  The pixel 20 includes a pixel electrode 21, a common electrode 22, an electrophoretic element 23, a pixel switching transistor 24, and a storage capacitor 25. The pixel switching transistor 24 is composed of, for example, an N-type transistor. The pixel switching transistor 24 is preferably composed of a TFT (Thin Film Transistor). The gate of the pixel switching transistor 24 is electrically connected to the scanning line (Y1, Y2,... Ym) of the corresponding row. The source of the pixel switching transistor 24 is electrically connected to the data line (X1, X2,... Xn) of the corresponding column. The drain of the pixel switching transistor 24 is electrically connected to the pixel electrode 21 and the storage capacitor 25. The pixel switching transistor 24 receives the image signal supplied from the data line driving circuit 3 via the data lines (X1, X2,... Xn) and the scanning line (Y1, Y2, Y2) of the corresponding row from the scanning line driving circuit 4. ... Are outputted to the pixel electrode 21 and the storage capacitor 25 at a timing according to the scanning signal supplied in a pulse manner via Ym).

  An image signal is supplied to the pixel electrode 21 from the data line driving circuit 3 through the data lines (X1, X2,... Xn) and the pixel switching transistor 24. The pixel electrode 21 is disposed opposite to the common electrode 22 with the electrophoretic element 23 interposed therebetween. The common electrode 22 is electrically connected to the common potential line 11 to which the common potential Vcom is supplied.

  The electrophoretic element 23 is a liquid containing a plurality of electrophoretic particles, and is held between electrodes so as not to leak with a sealing material (not shown).

  The storage capacitor 25 is composed of a pair of electrodes that are arranged to face each other with a dielectric film therebetween, one electrode is electrically connected to the pixel electrode 21 and the pixel switching transistor 24, and the other electrode is connected to the common potential line 11. Electrically connected. The storage capacitor 25 can maintain the image signal for a certain period.

  Next, a specific configuration of the display unit 2 of the electrophoretic display device 1 will be described with reference to FIG. FIG. 3 is a partial cross-sectional view of the display unit 2 in the electrophoretic display device 1. The display unit 2 has a configuration in which an element substrate 28 and a counter substrate 29 are arranged to face each other via a spacer (not shown), and an electrophoretic element 23 is sealed between the substrates. In the present embodiment, description will be made on the assumption that an image is displayed on the counter substrate 29 side.

  The element substrate 28 is a substrate made of, for example, glass or plastic. Although not shown here on the element substrate 28, the pixel switching transistor 24, the storage capacitor 25, the scanning lines (Y1, Y2,... Ym), and the data lines (X1, X2) described above with reference to FIG. ,... Xn), and a laminated structure in which the common potential line 11 is formed. A plurality of pixel electrodes 21 are provided in a matrix on the upper layer side of the stacked structure.

  The counter substrate 29 is a light transmissive substrate made of, for example, glass or plastic. On the surface of the counter substrate 29 facing the element substrate 28, the common electrode 22 is formed so as to face the plurality of pixel electrodes 21. The common electrode 22 is formed of a transparent conductive material such as magnesium silver (MgAg), indium tin oxide (ITO), indium zinc oxide (IZO), for example.

  The electrophoretic element 23 is an electrophoretic display liquid composed of positively charged black particles 83, negatively charged white particles 82, and a dispersion medium 81 that disperses the black particles 83 and the white particles 82. The element substrate 28 and the counter substrate 29 are enclosed. In addition, a spacer (not shown) is provided between the element substrate 28 and the counter substrate 29 to keep the gap between the substrates at a specified value, and a sealing material (not shown) for sealing the gap is provided on the end surface of the substrate. Is provided.

  In FIG. 3, when a voltage is applied between the pixel electrode 21 and the common electrode 22 so that the potential of the common electrode 22 is relatively high, the positively charged black particles 83 are caused by Coulomb force. While attracted to the pixel electrode 21 side, the negatively charged white particles 82 are attracted to the common electrode 22 side by Coulomb force. As a result, white particles 82 gather on the display surface side (the common electrode 22 side), and the display surface of the display unit 2 displays white. On the other hand, when a voltage is applied between the pixel electrode 21 and the common electrode 22 such that the potential of the pixel electrode 21 is relatively high (so that the potential of the common electrode 22 is relatively low). The positively charged black particles 83 are attracted to the common electrode 22 side by the Coulomb force, and the negatively charged white particles 82 are attracted to the pixel electrode 21 side by the Coulomb force. As a result, the black particles 83 gather on the display surface side (common electrode 22 side), and the display surface of the display unit 2 is displayed in black.

  In addition, by changing the pigment used for the white particles 82 and the black particles 83 to pigments such as red, green, and blue, for example, the display surface of the display unit 2 can be displayed in red, green, and blue. .

  Further, when the particles are placed under the same electric field, the moving speeds of, for example, white particles and black particles differ depending on the size of the particles and other factors. In the present embodiment, it is assumed that white particles are faster in moving speed than black particles.

  Next, a driving method for realizing suitable gradation display in the electrophoretic display device 1 configured as described above will be described. As an example, the resolution of gradation display is pure black display (lowest saturation reflectance) at the first gradation and pure white display (highest saturation reflectance) at the 16th gradation. Further, the pixel that should display the first gradation is associated with the pixel 1, the pixel that should display the second gradation, the pixel 2, and so on.

  With reference to FIG. 4 and FIG. 5, a driving method for realizing a desired gradation display for the pixels 1 to 16 will be described. FIG. 4 is a flowchart for changing the pixel 1 to the pixel 16 to the required gradation, and FIG. 5 is a gradation transition diagram corresponding to the flowchart shown in FIG. In FIG. 5, numbers 1 to 16 shown at the left end in the vertical direction (vertical axis) correspond to pixel numbers, and the horizontal axis corresponds to gradation. Pixel 1 to pixel 16 correspond to the pixel 20 shown in FIG.

  First, all the pixels 1 to 16 are reset to black display (first gradation: lowest saturation reflectance) (step S1). Therefore, the low potential VL is applied to the common electrode 22 and the high potential VH is applied to the pixel electrode 21 for all the pixels 1 to 16. Immediately after the reset in step S1, all the pixels 1 to 16 are displayed in black (first gradation).

  Next, white writing is performed once for all the pixels 1 to 16 (step S2). In white writing, a high potential VH is applied to the common electrode 22, a low potential VL is applied to the pixel electrode 21, and a standard selection pulse serving as a scanning signal is applied to the gate of the pixel switching transistor 24 of the writing target pixel 20. The first voltage pulse applied between the pixel electrodes is generated by the potential applied to the common electrode 22, the potential applied to the pixel electrode 21, and the standard selection pulse applied to the gate of the pixel switching transistor 24. Is done. The pulse length of the standard selection pulse is, for example, 40 μsec, and the selection time that is the white writing time to the pixel 20 is 40 μsec. The scanning line driving circuit 4 scans all the pixels 1 to 16 once by applying a standard selection pulse to the pixels 1 to 16 in order. The white display by the standard selection pulse changes the gradation display of all the pixels 1 to 16 to “white once” shown in FIG. As a result, the pixel 1 and the pixel 2 reach the first display state as shown in FIG.

  Here, the significance of resetting all the pixels 1 to 16 to black display before white writing will be described. FIG. 6 shows the change characteristics (black reference) when the gradation of the pixel 20 from the black display state to the white display is repeated by repeating the white writing scan, and the black writing scan from the white display state of the pixel 20. The change characteristic (white reference) when the gradation is changed to black display repeatedly is shown. It can be seen that the difference in change rate between the first scan and the second scan is larger in the change characteristic in the black reference than in the change characteristic in the white reference. From this, it can be seen that the black reference has a wider range of reflectance selection by the combination of the number of scans than the white reference. Therefore, since the selection range of the reflectance is wide by changing the gradation from the black reference (black display), it is easier to realize the required gradation.

  Further, a shaking pulse may be applied to all the pixels 1 to 16 before white writing is performed once in step S2. A driving circuit including the data line driving circuit 3, the scanning line driving circuit 4, the common potential supply circuit 5, the controller 6 and the like has a pixel electrode 21 of each pixel 20 with respect to all pixels serving as a control target area or pixels in a predetermined area. And a common electrode 22 are applied with a shaking pulse in which the polarity of the voltage is alternately inverted in a short time.

  Next, the second white writing is performed on the pixels 3 to 16 excluding the pixels 1 and 2 (step S3). The scanning line driving circuit 4 scans all the pixels 3 to 16 once by applying a standard selection pulse to the pixels 3 to 16 in order. By the second white writing, the gradation display of the pixels 3 to 16 is changed to “twice white” shown in FIG. The reason why the gradation change amount due to the second white writing is smaller than the first white writing is because the change amount of the second scanning is smaller than that of the first scanning in the black reference as shown in FIG. By the second white writing, the pixels 11 to 15 reach the first display state.

  Next, the third white writing is performed on the pixels 3 to 10 and the pixel 16 (step S4). The scanning line driving circuit 4 scans all the pixels 3 to 10 and 16 once by applying a standard selection pulse to the pixels 3 to 10 and the pixel 16 in order. By the third white writing, the gradation display of the pixels 3 to 10 and 16 is changed to “white three times” shown in FIG. The amount of gradation change due to the second white writing is smaller than the second white writing. By the third white writing, the pixels 3 to 10 and the pixel 16 reach the first display state.

  Next, minute black writing is performed on the pixels 1 to 12 with a second voltage pulse having a polarity opposite to that of the first voltage pulse, and the gradation display of the pixels 1 to 12 is turned back to the black display side. Here, in the fine black writing, the entire scanning time is left as it is, the selection time of the writing target pixel 20 is shortened, and the voltage applied to the pixel electrode 22 is equivalently lowered to perform black writing. The reason why the applied voltage is equivalently lowered is to facilitate delicate gradation control. In this example, the micro black writing is realized by applying a micro selection pulse having a selection time (for example, 10 μsec) smaller than the standard selection time (40 μsec) by the standard selection pulse. In addition, since black writing is applied, a low potential VL is applied to the common electrode 22 and a high potential VH is applied to the pixel electrode 21, and a minute selection pulse is applied to the gate of the pixel switching transistor 24 of the writing target pixel 20. To do. A second voltage pulse is generated by the minute selection pulse for minute black writing, the applied potential of the common electrode 22, and the applied potential of the pixel electrode 21.

  The first minute black writing is performed on the pixels 1 to 12 which are the pixels to be folded to the black display side (step S5). The scanning line driving circuit 4 scans the pixels 1 to 12 once by applying minute selection pulses to the pixels 1 to 12 in order. For example, the pixel 12 shown in FIG. 5 shows a gradation position that is turned back by a minute black writing from the gradation position of white twice to the black display side.

  Similarly, in steps S6 to S15, the second to eleventh micro black writes are performed from pixel 2 to pixel 12 while the final pixel number is decreased by 1 each time the step number increases. The gradation display of the pixel 1 to the pixel 12 shown in FIG. 5 is the gradation when the minute black writing is stopped.

  Through the above gradation control, gradation display from the pixel 1 to the twelfth gradation can be displayed from the first gradation to the twelfth gradation.

  Next, minute white writing is performed on the pixels 13 to 16 with a third voltage pulse having the same polarity as the first voltage pulse and a short selection time, and the gradation display of the pixels 13 to 16 is white. Add gradation to the display side. Here, in the fine white writing, similarly to the fine black writing, the entire scanning time is left as it is, the selection time of the pixel 20 to be written is shortened, and the voltage applied to the pixel electrode 22 is equivalently lowered, and the white is written. Write. A third voltage pulse is generated by a minute selection pulse for minute white writing, an applied potential of the common electrode 22, and an applied potential of the pixel electrode 21.

  The first minute white writing is performed on the pixels 13 to 16 which are pixels to be added to the white display side (step S16). The scanning line driving circuit 4 scans the pixels 13 to 16 once by applying minute selection pulses to the pixels 13 to 16 in order. For example, the pixel 13 shown in FIG. 5 shows a gradation position that is added by one minute white writing from the gradation position of white twice to the white display side.

  Similarly, in steps S17 to S20, the second to the fifth minute white writing is performed on the pixels 13 to 16 while the start pixel number is incremented by 1 each time the step number increases. The gradation display of the pixels 13 to 16 shown in FIG. 5 is the gradation when the minute white writing is stopped when the target gradation is reached.

  With the above gradation control, the gradation display from the pixel 13 to the 16th gradation can be displayed from the 13th gradation to the 16th gradation.

  That is, by combining white writing by the standard selection time, minute black writing and minute white writing by the minute selection time, and selecting a pixel to be folded to the black display side and a pixel to be added to the white display side, The gradation display from 1 to pixel 16 can be displayed from the first gradation to the 16th gradation.

  FIG. 7 is a diagram showing combinations of the number of times of white writing, the number of times of minute black writing, and the number of times of minute white writing when the pixels 1 to 16 are displayed from the first gradation to the 16th gradation. In FIG. 7, the left end on the horizontal axis corresponds to the pixel 1, and the right end corresponds to the pixel 16.

  In the above description, the case where gradation display that linearly changes from the first gradation to the 16th gradation is performed on the 16 pixels from pixel 1 to pixel 16 has been described. According to the present embodiment, a desired gradation display can be performed on a desired pixel in accordance with an arbitrary display image, and a gradation display in which the display image is reproduced with high accuracy is possible.

  As described above, according to the first embodiment, multi-gradation can be realized without increasing the required performance for the switching element or driver for controlling the pulse length or application timing applied to the pixel electrode, and high quality. An image can be displayed.

Next, an electrophoretic display device according to a second embodiment of the invention will be described.
The configuration and basic operation of the electrophoretic display device according to the second embodiment are the same as those of the electrophoretic display device according to the first embodiment described above. Here, a driving method for realizing required gradation display of the electrophoretic display device according to the second embodiment will be described.

  In the first embodiment, after white writing with a standard selection time (40 μsec), black or white writing with a minute selection time (10 μsec) is performed to obtain a required gradation display. However, it is difficult to realize writing with a very small selection time (10 μsec) because of the type of TFT constituting the pixel switching transistor 24 and the transfer speed of the image data of the display image, and the standard selection time (40 μsec). There may be a case where the minimum selection time is unavoidable.

  In the second embodiment, the pixel selection time (corresponding to the gate ON period of the pixel switching transistor 24) is not made shorter than the standard selection time (40 μsec), and the same gray scale display as in the first embodiment is performed. Is an example of

  Therefore, in the second embodiment, the standard selection time (40 μsec) is applied as the pixel selection time, and the scanning cycle (voltage pulse repetition cycle) is set to twice the cycle of the first embodiment. Thus, it is equivalently reduced to a level equivalent to the voltage at the time of writing with a minute selection time (10 μsec), and a fine gradation display is realized. FIG. 11A shows the voltage between the electrodes when a standard selection pulse having a pulse width of the standard selection time (40 μsec) is repeatedly applied to the gate of the pixel switching transistor 24 of the pixel 20 in the scanning period T. Yes. In the scanning cycle T, the next standard selection pulse is applied before the voltage drops sufficiently, so the average voltage level is V1. In FIG. 11B, a standard selection pulse having a pulse width of a standard selection time (40 μsec) is repeated with respect to the gate of the pixel switching transistor 24 of the pixel 20 in a cycle T2 (2 × T) which is twice the scanning cycle T. The voltage between the electrodes when applied is shown. In the scanning cycle 2T, which is a double cycle, since the next standard selection pulse is applied after the voltage is sufficiently lowered, the average voltage level V2 is lower than V1 shown in FIG. 11A. This embodiment utilizes the fact that the voltage between the electrodes decreases when driven at a scanning cycle T2 that is twice the scanning cycle T than when driven at the scanning cycle T.

  With reference to FIGS. 8 and 9, a driving method for realizing a desired gradation display for the pixels 1 to 16 will be described. FIG. 8 is a flowchart for changing the pixel 1 to the pixel 16 to the required gradation, and FIG. 9 is a gradation transition diagram corresponding to the flowchart shown in FIG. In FIG. 8, numbers 1 to 16 shown at the left end in the vertical direction (vertical axis) correspond to pixel numbers, and the horizontal axis corresponds to gradation. Pixel 1 to pixel 16 correspond to the pixel 20 shown in FIG.

  First, all the pixels 1 to 16 are reset to black display (first gradation) (step S21). Therefore, the low potential VL is applied to the common electrode 22 and the high potential VH is applied to the pixel electrode 21 for all the pixels 1 to 16. Immediately after the reset in step S21, all the pixels 1 to 16 are displayed in black (first gradation).

  In addition, a shaking pulse may be applied to all the pixels 1 to 16 before white writing is performed once in step S22. A driving circuit including the data line driving circuit 3, the scanning line driving circuit 4, the common potential supply circuit 5, the controller 6 and the like has a pixel electrode 21 of each pixel 20 with respect to all pixels serving as a control target area or pixels in a predetermined area. And a common electrode 22 are applied with a shaking pulse in which the polarity of the voltage is alternately inverted in a short time.

  Next, white writing is performed once for all the pixels 1 to 16 (step S22). In white writing, a high potential VH is applied to the common electrode 22, a low potential VL is applied to the pixel electrode 21, and a standard selection pulse serving as a scanning signal is applied to the gate of the pixel switching transistor 24 of the writing target pixel 20. The pulse width of the standard selection pulse is 40 μs, for example, and the selection time that is the white writing time to the pixel 20 is 40 μs. The first voltage pulse is generated by the applied potential of the common electrode 22, the applied potential of the pixel electrode 21, and the standard selection pulse (scanning cycle T1). The standard selection pulse scanning line driving circuit 4 scans all the pixels 1 to 16 once by applying the standard selection pulse to the pixels 1 to 16 in order. At this time, the scanning time required to scan the entire screen once is T1. By the white writing by the standard selection pulse, the gradation display of all the pixels 1 to 16 changes to “white once” shown in FIG.

  Next, the second white writing is performed on the pixels excluding the pixel 1, the pixel 8, and the pixel 12 (step S22). Thereafter, as shown in FIG. 9, the pixel is selected, and the third to sixth white writing is performed on the selected pixel (steps S23 to S27). The scanning cycle from step S22 to step S27 is T1.

  Next, double period black writing is performed with a scanning period T2 that is twice the scanning period T1 for the pixel that returns the gradation display to the black display side. As described above, even when double period black writing is performed in the scanning period T2, the selection time of the pixel 20 is 40 μs by the standard selection pulse. A second voltage pulse is generated by the standard selection pulse at the time of double period black writing, the applied potential of the common electrode 22, and the applied potential of the pixel electrode 21.

  As shown in FIG. 9, the pixel is selected, the entire screen is scanned at the scanning period T2, and the first to fourth double period black writing is performed on the selected pixel (steps S28 to S31). The voltage (V2) between the electrodes for writing is lower than the voltage (V1) between the electrodes at the time of black writing in the scanning cycle T1 during the first to fourth double cycle black writing in the scanning cycle T2. Compared with black writing in the scanning period T1, fine gradation display is possible.

  With the above gradation control, gradation display from the pixel 1 to the seventh and pixels 9 to 11 is completed.

  Next, gradation is added from the pixel 12 to the pixel 16 toward the white display side. Double period white writing is performed on the pixel to be added to the white display side at a scanning period T2 that is twice the scanning period T1. The selection time of the pixel 20 is 40 μs which is a standard selection time. A third voltage pulse is generated by the standard selection pulse at the time of double period white writing, the applied potential of the common electrode 22, and the applied potential of the pixel electrode 21.

  As shown in FIG. 9, the pixel is selected, the entire screen is scanned at the scanning cycle T2, and the first to seventh double cycle white writing is performed on the selected pixel (steps S32 to S38). Since the voltage (V2) between the electrodes for writing is lower than the voltage (V1) between the electrodes at the time of white writing in the scanning cycle T1 during the first to seventh white writing in the scanning cycle T2, scanning is performed. Compared with white writing in the period T1, fine gradation display is possible.

  With the above gradation control, the gradation display from the pixel 13 to the 16th gradation can be displayed from the 13th gradation to the 16th gradation.

  In other words, white writing by the standard selection time, double cycle white writing in which the scanning cycle is doubled while maintaining the standard selection time, and double cycle black writing in which the scanning cycle is doubled while maintaining the standard selection time are combined into the black display side. By selecting the return target pixel and the target pixel to be added to the white display side, the gradation display from pixel 1 to pixel 16 can be displayed from the first gradation to the 16th gradation.

  FIG. 10 is a diagram showing a combination of the number of white writing times, the number of black writing times, the number of times of double white writing, and the number of times of double black writing when the pixels 1 to 16 are displayed in the first to 16th gradations. In FIG. 10, the left end on the horizontal axis corresponds to the pixel 1 and the right end corresponds to the pixel 16.

  As described above, according to the second embodiment, since the voltage applied between the electrodes of the target pixel is controlled by combining the scanning periods with the standard selection time, the required performance for the switching element or driver is increased. Therefore, multi-gradation can be realized and a high-quality image can be displayed. In particular, the standard selection time (40 μsec) is set as the minimum selection time even when writing with a very small selection time (10 μsec) is difficult due to the type of TFT and the transfer rate of the image data of the display image. Gradation can be realized and high quality images can be displayed.

  In addition, this invention is not limited to the said embodiment, It can implement variously. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited thereto, and can be appropriately changed within a range in which the effect of the present invention is exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

DESCRIPTION OF SYMBOLS 1 Electrophoretic display apparatus 2 Display part 3 Data line drive circuit 4 Scan line drive circuit 5 Common electric potential supply circuit 6 Controller 11 Common electric potential line 20 Pixel 21 Pixel electrode 22 Common electrode 23 Electrophoretic element 24 Pixel switching transistor 25 Retention capacity 28 Element substrate 29 Counter substrate 81 Dispersion medium 82 White particles 83 Black particles

Claims (6)

At least one of the pair of substrates having light transparency, a plurality of pixel electrodes formed on a substrate surface of one of the pair of substrates, and the plurality of pixels on the substrate surface of the other substrate of the pair of substrates A liquid electrode formed by dispersing at least two kinds of charged particles having different moving speeds enclosed in a space formed between the pair of substrates, and the pixel electrode. And a drive circuit for generating a selection signal for selecting a target pixel to which the voltage pulse is to be applied, and generating a voltage pulse that generates a potential difference for moving the charged particles between the common electrode and the common electrode,
The drive circuit is
The first voltage pulse is applied to the target pixel a number of times determined according to the target gradation of the pixel, and the target pixel is changed to the first display state, and the target gradation is the first voltage pulse as viewed from the first display state. If the direction is the reverse of the direction of gradation change due to, the second voltage pulse having a polarity opposite to that of the first voltage pulse and having a smaller amount of gradation change per time than the first voltage pulse is selected as the target. If the target gradation is applied in the number of times corresponding to the gradation distance to the gradation and the target gradation is in the same direction as the gradation change direction by the first voltage pulse as seen from the first display state, it is the same as the first voltage pulse. An electrophoretic display characterized in that a third voltage pulse having a polarity and a gradation change amount per time smaller than that of the first voltage pulse is applied a number of times corresponding to the gradation distance to the target gradation. apparatus. The drive circuit is
The electrophoretic display device according to claim 1, wherein a voltage pulse having a pixel selection time shorter than that of the first voltage pulse is generated as the second and third voltage pulses. The drive circuit is
As the second and third voltage pulses, a voltage pulse having the same pixel selection time as the first voltage pulse is generated, and a repetition cycle when the second and / or third voltage pulses are applied multiple times, The electrophoretic display device according to claim 1, wherein the electrophoretic display device is longer than a repetition period of the first voltage pulse. The drive circuit is
The charged particles having a low moving speed are collected on the electrode on the substrate side having light permeability by applying a reset pulse to the target pixel before the transition to the first display state. The electrophoretic display device according to claim 3. The drive circuit is
A shaking pulse whose polarity of voltage is alternately inverted is applied between the pixel electrode and the common electrode of each pixel with respect to all the pixels to be controlled or all of the pixels in a predetermined area. The electrophoretic display device according to any one of claims 1 to 4. A pair of substrates at least one of which is light transmissive, a plurality of pixel electrodes on a substrate surface of one of the pair of substrates, and a plurality of pixel electrodes on a substrate surface of the other substrate of the pair of substrates A liquid electrode formed by dispersing at least two kinds of charged particles having different moving speeds enclosed in a space formed between the pair of substrates, the pixel electrode and the common electrode An electrophoretic display device comprising: a drive circuit that generates a voltage pulse that generates a potential difference for moving the charged particles between the electrode and a selection signal that selects a target pixel to which the voltage pulse is to be applied. In the driving method of
The first voltage pulse is applied to the target pixel a number of times determined according to the target gradation of the pixel, and the target pixel is changed to the first display state, and the target gradation is the first voltage pulse as viewed from the first display state. If the direction is the reverse of the direction of gradation change due to, the second voltage pulse having a polarity opposite to that of the first voltage pulse and having a smaller amount of gradation change per time than the first voltage pulse is selected as the target. If the target gradation is applied in the number of times corresponding to the gradation distance to the gradation and the target gradation is in the same direction as the gradation change direction by the first voltage pulse as seen from the first display state, it is the same as the first voltage pulse. An electrophoretic display characterized in that a third voltage pulse having a polarity and a gradation change amount per time smaller than that of the first voltage pulse is applied a number of times corresponding to the gradation distance to the target gradation. Device driving method.

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